OutputStream

Status: Experimental

present and registered, but lightly documented and not yet covered by dedicated tests.

Description

OutputStream["name", n]

is an object representing an open output stream, as returned by OpenWrite or OpenAppend. The integer n is an internal handle into the stream registry.

Examples (3)

Every input below was run against the current Mathilda build and its output recorded.

Applications (3)

A stream object stays inert — it is a handle, not data

In[1]:= OutputStream["stdout", 1]
Out[1]= OutputStream["stdout", 1]

Its head is OutputStream

In[2]:= Head[OutputStream["file.txt", 3]]
Out[2]= OutputStream

A protected stream-object head

In[3]:= MemberQ[Attributes[OutputStream], Protected]
Out[3]= True

Implementation notes

Definition. OutputStream["name", n] is the inert object representing an open output stream, as returned by OpenWrite or OpenAppend. The string is the stream's name (a file name, or "stdout"/"stderr"); the integer n is an internal handle into the process-global stream registry. It is Protected, has no builtin of its own, and its docstring lives in info.c.

Representation. src/io/streams.c keeps a process-global registry of open streams. Each open stream is handed to the language as an OutputStream[name, id] object (its input counterpart is InputStream[name, id]), where id addresses the registry slot holding the live FILE*. The write and stream builtins (Write, WriteString, Close, ...) resolve a target by looking that id up in the registry, matching the head against the interned SYM_OutputStream. As a two-argument expression its Head is OutputStream.

Usage & limits. It is a handle, not data: you pass it to the write and stream builtins, and Close frees its registry slot. The integer handle is an internal detail, meaningful only to the registry within the same session. Constructing one by hand does not open a stream — a live object comes from OpenWrite/OpenAppend.

Attributes: Protected.

References

• Source: src/io/streams.c
• Specification index: Mathilda_spec.md

Notes & additional examples

Notes

OutputStream["name", n] is the object representing an open output stream: the string names it (a file, or "stdout"/"stderr") and the integer n is an internal handle into the process-global stream registry. A live object is produced by OpenWrite or OpenAppend (which need a writable file), then passed to Write, WriteString, or Close; the examples above therefore show only the inert object itself. The integer handle is an internal registry detail — constructing an OutputStream[...] by hand does not open anything.